Applicant hereby claims foreign priority benefits under 35 U.S.C. xc2xa7 119 of Swiss Patent Application No. 1934/199 filed 22 Oct. 1999 and PCT Application No. PCT/CH00/00454, filed 25 Aug. 2000, the disclosure of which is herein incorporated by reference.
1. Technical Field
This invention relates to methods for manufacturing welded tubes in general, and to methods for manufacturing welded tubes that include the transfer of tube bodies between a forming apparatus and a welding machine.
2. Background Information
There exists an increasing demand for a production plant for internal high pressure forming (xe2x80x9chydroformingxe2x80x9d) of elongated, longitudinally closed, essentially tubular bodies for the production of shaped parts. These bodies may be configured as tubes or hollow bodies with rotationally asymmetrical, or only partly rotationally symmetrical, cross-sections, and may be used for the widest variety of purposes. If the shaped parts fabricated by hydroforming are used, e.g., in a body structure of a car or lorry or other vehicle, the quality of the outer skin of the shaped parts is becoming increasingly important, as these are increasingly used as body components and are therefore visible on the finished body. Today, tubes with a length of approximately one (1) meter to four (4) meters and with diameter-to-thickness ratios of sixty (60) or more are being used for this purpose. However, it is likely that the lengths will continue to increase, and may exceed, e.g., five (5) meters, while the diameter-to-thickness ratios drop to forty (40) or less and also increase to one hundred (100), one hundred and fifty (150) or more. It is moreover likely that rotationally asymmetrical bodies will also be used, e.g., bodies with elliptical or oval cross-sections with partially flattened or parallel side wall parts, and/or bodies with rectangular or triangular cross-sections. The cross-section is governed by the specific application, which may demand every possible cross-sectional shape.
The initial material for such bodies to be processed by hydroforming into shaped parts is a flat sheet-metal blank which constitutes the shell of the future body. The blank is formed in a press or rounding apparatus into an elongated tubular body, which is not longitudinally closed, as the corresponding sheet-metal edges are adjacent but are not yet joined together. Joining is done by welding with an energy beam such as a laser or by some other suitable welding process while the longitudinal edges are held in the butt position. The quality of the weld seam is subject to special requirements, e.g., as to its fluid tightness and elasticity during the ensuing hydroforming.
Generally speaking, elongated welded tubular bodies need to be fabricated with a high quality welded joint and, depending on the application, with a high-quality outer skin, as scratches or indentations on the shaped parts are undesirable or unacceptable. Therefore the basic problem of the invention is to provide methods and apparatuses with which elongated tubular bodies, in particular with a high-quality outer skin, can be produced efficiently.
Hereinafter where mention is made of xe2x80x9ctubesxe2x80x9d, xe2x80x9ctube bodiesxe2x80x9d, etc., these are to be understood as signifying elongated tubular bodies with variously configured cross-sections according to the remarks made above.
A method for the manufacture of welded tubes is provided. The tube bodies are produced in a press or rounding apparatus and are fed to a welding machine, such as a laser or electron beam type welding machine. The tube is formed when the edges of the tube bodies are welded together. The method includes the transfer of the tube bodies from the press or rounding apparatus to the draw-in of the welding machine. One or more transfer modules, each having a separate drive, are used to convey the tube bodies. The one or more transfer modules, which are operated by a common control arrangement, are controlled so that the intermittently formed tube bodies are presented at the draw-in to the welding machine in as nearly continuous a sequence as possible.
Through the provision between the equipment for forming the tube bodiesxe2x80x94(which may be a press that forms the tube bodies in a number of bending steps, or a rounding apparatus)xe2x80x94on the one hand, and the welding machine on the other hand, of a number of transfer modules which are actuated by a common control so that the transfer modules can constitute a buffer between the equipment for forming the tube bodies and the actual welding machine, it becomes possible to harness an intermittent tube body production to a continuous welding operation. For example, three short tube bodies or one long tube body can be formed simultaneously in a press, and by slowing and/or accelerating individual tube bodies in the transfer line, can be arranged into a series of tube bodies that is as continuous and as closely spaced as possible on running through the welding zone.
With a continuous feed of tubes, it is also possible to configure the transfer line so that the tubes are presented in the welding zone for an optimal length of production run.
In accordance with a further aspect, an effort is made to transfer the tube bodies in such a way that their outer skin remains free from damage, and also in particular, that correct orientation of the edges is preserved during transfer, if need be with an initial squeezing of the tube body with a view to a subsequent closure of the gap in the welding area. Squeezing of the tubes may be advisable because after the plastic forming of the blank into a tube there is an elastic spring-back which opens up the gap between the edges somewhat. Also, the gap may be narrow enough or not quite narrow enough, depending on the method used for forming the blank. Furthermore, the use of different sheet-metal alloys and/or thicknesses on one and the same plant can result in different gaps, and this may need correcting in the subsequent processing of the tubular body.
The present method provides substantially damage-free transfer between the press or rounding apparatus and the welding machine by carrying the tube bodies on the inside of the tube during the transfer.
Supporting the bodies from inside protects the outer skin from damage. Means for locating the edges during transfer can also operate internally, or on the edges themselves. Such locating means, e.g., in the form of internally acting rollers and/or leaf spring devices acting on the edges, are advantageous in bringing the tube body to the draw-in to the welding machine ready orientated, so that at that point only slight adjustments of alignment are necessary in addition to the closure of the tubular body. It is also preferred that there be a facility for partially closing the gap in the body while transfer is still taking place, preferably by externally acting drive rollers whose mutual position is adjustable.
It is also desirable to ensure smooth, e.g., jolt-free, run-in of the tube bodies at the draw-in to the welding machine, or as they are passed from the transfer apparatus to the welding machine; even if the transfer apparatus does not assist further closure of a tube to be supplied which is inherently too wide open. It should be possible for the welding machine to handle the widest possible variety of tube dimensions and gap widths. Furthermore, it is advantageous that the quality of the outer skin of the tube should not be impaired by this operation.
The present method utilizes a draw-in means, in particular draw-in rollers, which receive the tube body in an open position of the draw-in means and then close to a predetermined setting to reduce the gap opening of the body and preferably to contact the body so as to advance it. The draw-in means move back to the open position after the body has passed through.
As the draw-in means are in an open position when they receive the tube body, abrupt impact of the body on these means, possibly damaging the outer skin, does not occur. The closing of the draw-in rollers to the predetermined setting, triggered by a tube body sensor, can be effected relatively gently so that the draw-in means or rollers, which are preferably plastic-coated or made of plastic material, do no damage to the outer skin of the body. In seizing the tubular body the draw-in means partially close the body while advantageously applying the force needed to propel the body through further stations of the welding machine as far as the next propelling means in the conveying direction.
In the manufacture of welded tubes, it is preferable to at least partly close the gap in the tube bodies before they reach the welding tool; advantageously, this should be done without damaging the outer skin of the bodies. The present method accomplishes this by at least largely closing the open body edges in the welding machine using a tool acting externally on the body with a predetermined setting. Preferably, the tool has a floating mount and/or assumes a basic position through spring force. In these embodiments, because the tool acting externally on the tube body to close the edges has a floating mount, it is able to follow any movements of the bodies about their longitudinal axis, and this largely excludes the possibility of damage to the outer skin of the body.
The tool is preferably adjustable over the circumference of the tube body, and of course adjustable in such a way that the object of largely closing up the edges is realized through a continuous, narrowing squeezing together of the body. This squeezing together is preferably performed against a tapering element that sets the edge-closure by plunging into the body, travelling with the body if need be, and (if so) provided with its own drive if need be. The edges must bear on this element, though not with large transverse forces. As the wall thickness of the tube bodies is variable, the transverse forces must also be adjustable, which is realized by setting the tool to the tapering diameter required. The tool may apply pressure to the body, e.g., by means of pneumatic cylinders.
At this juncture, a point should be noted that applies in principle to all stations in the welding plant: as the tube runs through, its shape changes in a way that is non-uniform over its length. If, say, the middle of a long tube is in the tool described above, a portion of the leading end is already welded, while the trailing end has a fully open gap. If the reshaping from front to rear is linear, it is so only by chance; the tube warps over its length, which adversely affects the position of the edges to be welded. What is more, the warping changes as welding progresses. Also, the warping is dependent on, e.g., the length, material and thickness of the tube. In other words, the tube is xe2x80x9calivexe2x80x9d during processing, which may in particular compromise the edge position that is required for welding.
Another issue that must be addressed in the manufacturing of tubes is that the edges to be welded must be guided to a correct position for welding. The welding requires an edge closure with an extremely small tolerance, which in the case of laser welding for example amounts to only 0.08 mm.
The present method addresses this issue by utilizing a closing tool with one or more, preferably exchangeable, modules. Each module has rollers that are arranged in a ring and are adapted to the tube cross-section. At least one of the rollers is adjustably mounted so that, over its range of adjustment no damage is caused to the tube body, especially to the outer skin thereof, by its action on the body, owing to the change in position.
Through provision in the welding zone of a welding tool formed from modules with rings of rollers, the requisite number of rollers can be provided for each sheet-metal thickness and grade. These rollers may be driven, and have the particular function of setting a defined edge position during welding.
Preferably, spring-mounted lower rollers may be provided to effect a squeezing together of the tube body edges to close the gap as nearly completely as possible, but at least to within the range of tolerance for laser welding. Squeezing the edges together evens out cuffing variations or waviness of the edges, but on the other hand it usually causes V-shaped splaying of the edges, which may be undesirable. This can be prevented by the upper rollers, which guide and/or press the edges so that the edge faces are in contact with each other. The preferred mounting for the upper and lower rollers is one which prevents the rims of the waisted rollers from leaving impressions in the tube body surface.
By providing a plurality of modules, various actions can be performed on the tube body by means of the rollers of these modules and a good adaptation can be made to tubes that are difficult to Weld (owing to material, dimensions, surface coating) by adding or removing modules to obtain an optimal effect on the tube body.
After welding, there is usually an inspection of the welded joint or seam quality. It is preferred that a drive be provided, preferably in the form of a further roller ring module, to advance the tube into the zone where the (usually optical) inspection of seam quality takes place, so that the tube is guided and driven in this area also, this being beneficial for the inspection, which is sensitive to vibrations, i.e. reacts to positional fluctuations (positional variations) of the seam.